Just a basic geiger counter I made. The boost converter is just based off the topology from the Wikipedia article, made of a 600v 2A MOSFET, 600v 1A diode, 100mH inductor, and the switching signal is coming from an ATtiny13, at about 99.2% duty cycle and 2500Hz. This provides the 470vdc needed for the geiger tube from as low as about 3vdc. The voltage output is regulated by 5 100v zener diodes in series, and is fed through a 10M current limiting resistor to the anode of the geiger tube, and the cathode connects to ground through a 470k resistor. The signal is pulled at the junction of the cathode and 470k resistor, and is a 9v exponentially decreasing signal that lasts 300uS. This signal is directly fed to the gate of a MOSFET, which allows current to flow through a speaker, causing the audible clicks. The radiation source is the tiny dot of Americium 241 found in ionizing smoke detectors. The geiger tube was purchased from Electronics Goldmine for , and I’d guess that collectively the other parts cost around total. Most of the information I needed came from here: www.imagesco.com and several sites for the boost converter.